The broad, long-term objective of the proposed project is to enhance current understanding of relapse to alcohol and other drug problems, and to improve treatment and prevention strategies. The first aim of this research is to empirically refine the construct of experiential avoidance, which has recently gained a great deal of attention in relation to substance use, and psychopathology, more generally. This involves the development and validation of a measure of experiential avoidance in an undergraduate sample and the replication of these procedures in a sample of individuals with substance use disorders. The procedures involved include, an exploratory factor analysis of a combined pool of items measuring avoidance processes, a confirmatory factor analysis of the derived factors in an independent sample, convergent and discriminant validation, and establishing relationships among identified factors and substance use. The final aim of the proposed project is to evaluate experiential avoidance as a mediator and a moderator of treatment efficacy as part of a randomized controlled trial comparing mindfulness-based relapse prevention (MBRP), to cognitive-behavioral relapse prevention (RP), and treatment as usual (TAU). Participants will be individuals enrolled in continuing care following intensive outpatient treatment, and will be assessed at baseline, mid-treatment, post-treatment, and 2- and 4-months following treatment. It is expected that rates of relapse will decrease as a function of reductions in experiential avoidance, across interventions. It is also expected that reductions in experiential avoidance will mediate treatment efficacy, especially for the MBRP group, which focuses directly on countering avoidance through training in mindfulness. Finally, it is expected that individuals who are higher on baseline experiential avoidance will demonstrate better outcomes in the MBRP condition, relative to RP alone, and TAU. This research builds on prior research that aims to identify the active ingredients of evidence-based interventions. The findings of this research will aid in achieving a more thorough understanding of the factors related to relapse, and in increasing the overall effectiveness of interventions. [unreadable] [unreadable] [unreadable]